1. Technical Field
The present invention relates to a method for fabricating a thin film transistor (TFT) for use with a flat panel display device. In particular, the present invention relates to a method for fabricating a TFT with a reduced number of masks.
2. Related Art
Image display devices for use with portable information devices are in demand. In particular, flat panel displays (FPD) replacing cathode ray tubes (CRT) are in a strong demand. A liquid crystal display (LCD) is one of the most popular flat panel displays (FPD). An LCD device displays images by using optical anisotropy of liquid crystal. An LCD device has been in use as monitors of a notebook computer and a desktop computer because it provides advantages of high resolution and good picture quality.
An LCD device includes a first substrate of a color filter substrate; a second substrate of an array substrate; and a liquid crystal layer formed between the color filter substrate and the array substrate. An LCD device is fabricated with the photolithography. The photolithography involves a plurality of mask processes for the array substrate including a thin film transistor which functions as a switching element.
FIG. 1 is a plane view illustrating some portions of a thin film transistor array substrate for use with an LCD device. In FIG. 1, a line I-I′ corresponds to a thin film transistor part and a data line part, a line II-II′ corresponds to a data pad part, and a line III-III′ corresponds to a gate pad part.
The related art method for fabricating the LCD device may involve a number of masks, e.g., four, five, or six masks depending on model. For example, in FIG. 1, the related art method may use four masks, including (i) a first mask for forming a gate electrode 3P2, a gate line 3P and a gate pad 3P1 on a substrate 1, (ii) a second mask for forming an active layer (not shown), a data line 9P, data pad 9P1 and source and drain electrodes 9P2 and 9P3, (iii) a third mask for forming a contact hole in a passivation layer (not shown), and (iv) a fourth mask for forming a pixel electrode 15P.
A mask used in the related art fabrication method of the LCD device may be an expensive item. Production cost may substantially increase as more masks are used in the fabrication method. When a mask is used, additional process such as irradiating, stripping and cleaning follows. Accordingly, there is a need of simplifying a process for fabricating an LCD device, in particular, reducing a number of masks used in the fabrication method.